How to set empty password using pam_unix.so?

[Arek Marud]

Hi,

I'm trying to set empty password (or delete password) using pam_unix.so.
Basically I'm trying to emulate command "passwd -d <user>"

I'm able to change password to non-empty using pam_chauthtok function,
but so far no luck with empty one.

My program output:
```
New password: 
Password change aborted.
Authentication token manipulation error
```

This is my config:
```
#%PAM-1.0
auth    required    pam_unix.so nullok nodelay debug 
account required    pam_unix.so debug
password required    pam_unix.so debug  nullok
session required    pam_unix.so debug
```

-- 
Arek Marud